Hydrogen peroxide associated with ambient fine-mode, diesel, and biodiesel aerosol particles in Southern California

Abstract

To investigate the sources of H 2O 2 generation in fine-mode aerosols, a series of measurements on laboratory-generated particles, source materials, and ambient particles collected in the Los Angeles area were performed. Ambient fine-mode H 2O 2 levels were associated with transition metals, and were increased by the addition of dithiothreitol, a marker for quinone redox activity. H 2O 2 levels were sensitive to the pH of the particle extraction solutions, peaking in the pH range of 2.5-5.5. The initial rate of H 2O 2 generation by fine-mode ambient aerosols averaged 5.9 (±2.8) × 10 9 M min 1, in the range of the initial rates of H 2O 2 generation by active quinones and hydroxyl radical generation by transition metals. H 2O 2 levels were persistent, remaining nearly constant for about a week in ambient fine-mode particles. Laboratory experiments show that secondary organic aerosols and diesel and biodiesel exhaust particles generate as much or more H 2O 2 than ambient particles. These data indicate roles for metals such as iron, zinc, and copper, with additional sources, likely quinones and other unidentified organics, in the H 2O 2 generation by fine-mode aerosols. © 2012 Copyright Taylor and Francis Group, LLC.